title: Effects of noxious stimulation and pain expectations on neuromuscular control of the spine in patients with chronic low back pain.
abstract: BACKGROUND
  Alterations of the neuromuscular control of the lumbar spine have been reported in patients with chronic low back pain (LBP). During trunk flexion and extension tasks, the reduced myoelectric activity of the low back extensor musculature observed during full trunk flexion is typically absent in patients with chronic LBP.
  
  
  OBJECTIVE
  To determine whether pain expectations could modulate neuromuscular responses to experimental LBP to a higher extent in patients with chronic LBP compared with controls.
  
  
  METHODS
  A cross-sectional, case-control study.
  
  
  METHODS
  Twenty-two patients with nonspecific chronic LBP and 22 age- and sex-matched control participants.
  
  
  METHODS
  Trunk flexion-extension tasks were performed under three experimental conditions: innocuous heat, noxious stimulation with low pain expectation, and noxious stimulation with high pain expectation. Noxious stimulations were delivered using a contact heat thermode applied on the skin of the lumbar region (L4-L5), whereas low or high pain expectations were induced by verbal and visual instructions.
  
  
  METHODS
  Surface electromyography of erector spinae at L2-L3 and L4-L5, as well as lumbopelvic kinematic variables were collected during the tasks. Pain was evaluated using a numerical rating scale. Pain catastrophizing, disability, anxiety, and fear-avoidance beliefs were measured using validated questionnaires.
  
  
  RESULTS
  Two-way mixed analysis of variance revealed that pain was significantly different among the three experimental conditions (F2,84=317.5; p<.001). Increased myoelectric activity of the low back extensor musculature during full trunk flexion was observed in the high compared with low pain expectations condition at the L2-L3 level (F2,84=9.5; p<.001) and at the L4-L5 level (F2,84=3.7; p=.030). At the L4-L5 level, this effect was significantly more pronounced for the control participants compared with patients with chronic LBP (F2,84=3.4; p=.045). Pearson correlation analysis revealed that increased lumbar muscle activity in full flexion induced by expectations was associated with higher pain catastrophizing in patients with chronic LBP (r=0.54; p=.012).
  
  
  CONCLUSIONS
  Repeated exposure to pain appears to generate rigid and less variable patterns of muscle activation in patients with chronic LBP, which attenuate their response to pain expectations. Patients with high levels of pain catastrophizing show higher myoelectric activity of lumbar muscles in full flexion and exhibit greater neuromechanical changes when expecting strong pain.
authors.affiliation: Département de chiropratique, Université du Québec à Trois-Rivières, 3351 boul. Des Forges, Trois-Rivières, G9A 5H7, Canada.
authors.forename: Yves
authors.initials: Y
authors.lastname: Henchoz
authors.forename: Charles
authors.initials: C
authors.lastname: Tétreau
authors.forename: Jacques
authors.initials: J
authors.lastname: Abboud
authors.forename: Mathieu
authors.initials: M
authors.lastname: Piché
authors.forename: Martin
authors.initials: M
authors.lastname: Descarreaux
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D058443:Catastrophization / Q000503:physiopathology* / Q000523:psychology; D003430:Cross-Sectional Studies; D004576:Electromyography; D005260:Female; D006358:Hot Temperature; D006801:Humans; D017116:Low Back Pain / Q000150:complications* / Q000503:physiopathology; D008161:Lumbosacral Region / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010146:Pain / Q000503:physiopathology / Q000523:psychology*
keywords: Biopsychosocial outcomes; Chronic low back pain; Electromyography; Neuromuscular control; Pain expectations